Humans are exposed to genotoxic agents through a variety of sources including industrial processes, medical therapies, solar radiation and lifestyle factors including diet and tobacco use. It is important to develop biomarkers of DNA damage which evaluate exposure, effects and susceptibilities in human populations. Micronucleus (MN) formation is an important genotoxic endpoint which can be used to effectively detect DNA damage resulting from clastogenic or aneugenic mechanisms. Chromosomal damage of this type is closely associated with birth defects as well as cancer. A sensitive and high throughput system to measure human blood samples for MN would have a myriad of biomonitoring applications. For example, such a system could provide important information regarding the chromosome damaging activity of new drugs undergoing clinical trials, chemotherapy regimens, as well as accidental radiation or chemical exposures. This project is based on flow cytometry technology. The goals for Phase I are: 1) to recruit human subjects for peripheral blood sampling; 2) develop procedures to differentially label immature (RETs) and mature erythrocytes; and, 3) effectively enumerate micronuclei in RETs. Procedures will be based on an automated technique developed at Litron for detecting chromosome damage in rodent blood samples. PROPOSED COMMERCIAL APPLICATIONS: The successful development of this methodology will enable Litron Laboratories to become an expert facility, capable of performing cytogenetic measurements on human blood samples for clinical experiments on a fee- for-service basis. Additionally, by developing the necessary reagents into kit format, it would be possible to make this technology available to other laboratories having access to a single-laser flow cytometer. This technologically innovative technique has the potential to become an important clinical tool for measuring DNA damage.